UHF CB

Key takeaways

UHF CB belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect UHF CB to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of UHF CB from memory before moving on to harder problems.

Reference excerpt

UHF CB is a class-licensed citizen's band radio service authorised by the governments of Australia, Europe, Malaysia, New Zealand, Singapore, Vanuatu, and in the PMR446, UHF 477 MHz band. UHF CB provides 77 channels, including 32 channels (16 output, 16 input) allocated to repeater stations. It is similar in concept to the General Mobile Radio Service in the United States.

Equipment User equipment designs are similar to commercial land mobile two-way radio, except the maximum legal output power is 5 Watts. External antennas are permitted and commercially manufactured antennas have gains as high as 12 dB. Handheld transceivers (handy talkies) are permitted and have transmit power from 500 mW to 5 W (full legal power) and are relatively cheap compared to full-sized transceivers. Operation in the band is restricted to modes F3E and G3E (FM or PM of analogue voice telephony) except for channels 22 and 23, which are data modes only.

Licensing

Australia In Australia, class licensing means that users do not have to apply for a licence or pay a licence fee; however, they must comply with the regulations of the class licence. It is illegal to use non-standard radios purchased from outside Australia because they may interfere with licensed land-mobile services. This includes overseas personal radio service devices because they do not share the same band plan, power output and channels as UHF CB. Care must be taken when importing radios from overseas to ensure they comply with local regulations. Approved radios are identified by the Regulatory Compliance Mark (RCM) label, usually found on the rear panel of the equipment.

Scan Many UHF CB radios allow the user to scan channels to find a conversation. Several different scan modes may be provided: Open Scan scans all 80 channels to find an active conversation. Some radios allow skipping selected channels when scanning. Group Scan scans a small number of selected channels. For example, a caravanner travelling around the country may choose to group scan Channel 40 (Road Channel), 18 (Caravan Channel) and 5 (Emergency Channel) so they will hear any conversations relating to their travels. Priority Scan allows selection of a "priority" channel whilst scanning a handful of selected channels. This could be useful, for example, in a convoy of vehicles: convoy members can set their chosen convoy channel as a "priority" whilst scanning the designated road channel for traffic updates etc. If a convoy member speaks, the radio will switch back to the priority channel even if someone is speaking on another channel.

Selcall Selective calling (Selcall) allows a radio to call another radio using a sequence of tones, usually presented to the user as a series of 5 numbers. UHF CB radios can be set to be completely silent until they receive a series of tones matching a pre-programmed sequence. Radios which have this feature usually indicate that a call has been received by emitting a number of beeps and by opening the squelch. The popularity of selcall has dropped since the introduction of CTCSS.

CTCSS Continuous tone coded squelch system (CTCSS) allows a group of radios set with the same tone to converse on a channel without hearing other radios using that channel. CTCSS can be used to silence a radio until another radio with the same tone transmits. This allows monitoring of a channel for transmissions from radios set with the same tone without hearing other conversations that use different or even no tone. The use of CTCSS is not permitted on UHF CB repeaters or the designated emergency channels.

Repeaters Repeaters extend the range of transmission by receiving and automatically rebroadcasting a transmission using an antenna located in a high location, normally the top of a mountain, tall building or radio tower. Sometimes a transmission range of over 100 kilometres (60 miles) can be achieved through the use of a repeater. Repeaters are on channels 1–8 and 41–48 and the duplex button should be pressed to access the repeater. All repeaters can be used by anyone, except for channel 5 repeaters, which are for emergencies only.

Signage It is common practice to install signs at worksites, roadworks, regional highways, national parks, heavy vehicle checking stations, and on the rear of camper vans and caravans to advertise a UHF channel for communications. For example, during the widening of the M1 Pacific Motorway between Sydney and Newcastle, contractors installed "UHF 29" signs at the entry point of each worksite.

Channel use

Legally restricted channels The following channels are legislated as a part of the ACMA UHF CB Class Licence.

Channel 5 and 35 are the designated emergency channels in Australia, Vanuatu and Malaysia, and are not to be used except in an emergency. Making an emergency call involves switching the radio to Channel 5 with duplex on, and trying again with duplex off if there's no response. Some areas in Australia may not have someone monitoring channels 5 and 35. As well as private monitors, there are monitoring groups in Australia, notably, Radio Rescue Emergency Communications Inc., Australia Citizens Radio Monitors, South East Queensland Emergency Service Team, Citizens Radio Emergency Service Team South Australia, Citizens Radio Emergency Service Team Victoria, Citizens Radio Emergency Service Team New South Wales and Citizens Radio Emergency Service Team Queensland. In New Zealand channels 5 and 35 are not emergency channels but are available for general use in duplex (repeater) mode. In New Zealand, if you use UHF PRS for emergencies, you rely on someone listening on the same channel, and should scan all channels for activity before requesting assistance. Channel 9 is the designated emergency channel in Malaysia. Channel 11 is the 'call channel' and is only to be used for initiating calls with another person, who should quickly organise another vacant channel to continue their discussion, unlike New Zealand which uses channel 11 as its main trucking channel. Channel 22 and 23 are only to be used for telemetry and telecommand. Packet data and voice transmission are not allowed. Channel 61, 62 and 63 are reserved for future allocation and transmission on these channels is not allowed.

Channels used by consensus The following channels are not legislated as a part of the class licence however are used for the following purposes by consensus.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with UHF CB

Start with the simplest possible case. Write down what UHF CB claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to UHF CB before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about UHF CB ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of UHF CB

In research: UHF CB appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses UHF CB in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: UHF CB is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bandplans, Radio hobbies, so understanding it makes those chapters shorter.
In everyday life: Look for UHF CB outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study UHF CB in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what UHF CB means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain UHF CB out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is UHF CB in simple terms?

UHF CB is a class-licensed citizen's band radio service authorised by the governments of Australia, Europe, Malaysia, New Zealand, Singapore, Vanuatu, and in the PMR446, UHF 477 MHz band. UHF CB provides 77 channels, including 32 channels (16 output, 16 input) allocated to repeater stations.

Why does UHF CB matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study UHF CB?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on UHF CB.